1. Field of the Invention
The invention relates to a search method and a device thereof, and in particular relates to a packet preamble search method and a device thereof.
2. Description of the Related Art
In a communication system, a transmitted signal includes a desired transmitted payload, a destination address, and other extensions for specific purposes. For example, a transmitted signal may include an error detection/correction code (e.g., Cyclic Redundancy Check (CRC)) and a packet preamble for synchronization. The above-mentioned items are assembled into a single packet as shown in FIG. 1 before transmission. A format of the packet is illustrated in FIG. 1, wherein the packet comprises the packet preamble 11, the destination address 12, the payload 13, and the Cyclic Redundancy Check (CRC) 14. The packet is prefaced by the packet preamble to ensure that a starting point of the packet can be located and further to make the subsequent received signal understood by a receiver of the communication system. The packet preamble can be easily recognized by the receiver of the communication system as the packet preamble is coded with regular form. If the packet is transmitted directly without being prefaced by the packet preamble, noise intervening between the transmitted signal may coincide with the destination address. Thus the coincidence between the corrupted transmitted signal and the destination address will cause a false alarm. The probability of false alarms can be significantly reduced by prefacing the packet with the packet preamble, since false alarms will only happen when the corrupted transmitted signal matches the packet preamble and the destination address simultaneously. Accordingly, the packet preamble search becomes the most important topic during the process of disassembling the packet.
In the prior art, the signal of the same bit length as that of the packet preamble will be extracted from the received transmission signal for a complete bitwise pattern match, since searching the entire packet preamble by the receiver of the communication system is required to proceed with the subsequent disassembly work for the other components of the packet such as the destination address and the error detection/correction code. If the extracted signal matches the packet preamble exactly, the subsequent disassembly work for the other components of the packet will be processed. If any one bit of the extracted signal does not match that of the packet preamble, another series of signal of the same bit length with that of the packet preamble will be extracted from the received transmission signal for the pattern matching until the signal extracted from the received transmission signal matches the packet preamble. However, the transmitted signal will be interfered with by the noise when transmitted in a bad condition that makes the received transmission signal undesirable. The complete bitwise pattern match required by the conventional packet preamble search method is time consuming as the entire packet preamble must be searched, thus delaying the communication time and reducing the efficiency.